Conflicts of interest The authors declare no conflicts of interest.
Macroalgal turfs in the Azores
Article first published online: 25 SEP 2009
© 2009 Blackwell Verlag GmbH
Special Issue: Proceedings of the 43rd European Marine Biology Symposium, The Azores islands (Portugal), 8-12 September 2008
Volume 30, Issue Supplement s1, pages 113–117, October 2009
How to Cite
Wallenstein, F. M., Terra, M. R., Pombo, J. and Neto, A. I. (2009), Macroalgal turfs in the Azores. Marine Ecology, 30: 113–117. doi: 10.1111/j.1439-0485.2009.00311.x
- Issue published online: 25 SEP 2009
- Article first published online: 25 SEP 2009
- Calcareous turf;
- non-calcareous turf;
- rocky shores
Studies on macroalgal communities of the Azores report algal turfs as one of the most conspicuous ecological entities occurring on the rocky shores of these islands. The present study investigates the influence of shore height and substratum on turf composition. Data were analysed using the software PRIMER and results confirmed the previous distinction between calcareous, dominated by articulated coralline algae, and non-calcareous turfs, characterized mainly by small red algae. However, no differences in species composition were found in either type of turf occurring on different substrata or at different shore levels.
A suite of studies undertaken during the past 15 years has investigated the intertidal and subtidal algal communities of the Azores (Neto 1992, 2000, 2001; Neto & Tittley 1995; Tittley et al. 1998; Tittley & Neto 2000). Algal turfs are generally described as complex assemblages of macroalgae with compact growth, 5 cm in height and well developed entangled prostrate axes (Price & Scott 1992). Turfs are conspicuous features of warm temperate intertidal communities, and have been widely studied (Chapman 1955; Pryor 1967; Lawson & Norton 1971; Oliveira & Mayral 1976; Lawson & John 1977; Rogers & Salesky 1981; Stewart 1982; Neto & Tittley 1995; Morton et al. 1998). Some studies have classified communities systematically as biotopes based on broad ecological/taxonomic categories, such as green algae, calcareous and non-calcareous turfs and crusts (e.g.Neto & Tittley 1995; Tittley et al. 1998, Tittley & Neto 2000; Wallenstein & Neto 2006; Wallenstein et al. 2008). Turfs classified as calcareous or coralline occur with increasing abundance towards the low-shore and are usually not very conspicuous on less stable substrata such as cobbles, whereas turfs classified as non-calcareous are more evenly distributed across the intertidal with higher abundances at mid-shore (Neto & Tittley 1995; Wallenstein & Neto 2006; Wallenstein et al. 2008). Classification of turfs into these two broad categories has been based on the abundance of erect coralline algae (recognizable by the naked eye) and can thus be subjective and artificial. To evaluate whether such a classification is artificial we have tested differences between species composition in samples of turf provisionally identified in situ as calcareous (i.e. dominated by erect coralline algae) or non-calcareous turf.
Material and Methods
Data for analysis were gathered in the course of intertidal biotope surveys undertaken on three islands of the archipelago – São Miguel, Santa Maria and Graciosa (Fig. 1) in the summer periods of 2004, 2005 and 2006, respectively. As macroalgae communities are not evenly distributed across the intertidal, both in terms of species composition and substratum coverage, they pose a difficulty in sampling designs that require the collection of an equal number of samples at differing ‘substratum × shore level’ combinations. Although the original aim was to acquire quantitative data for macroalgal communities at high-, mid- and low-shore, on three substrata (cobbles, boulders and bedrock), high-shore samples had to be excluded from the pool of data because there were several sites where calcareous turf was absent. At mid- and low-shore, whenever possible two 10 × 10 cm areas (minimal intertidal scraping area defined by Neto 1997) of each type of turf (calcareous and non-calcareous) were cleared (scraped with a chisel into a nylon mesh bag) from the upper facing surfaces of three different substrata and brought to the laboratory for examination. Additionally, owing to an irregular distribution of substrata along the shores of the surveyed islands, an uneven sampling design had to be adopted (Table 1).
|Graciosa||Santa Maria||São Miguel||Total|
|Cobbles||22 (3 sites)||14 (4 sites)||28 (5 sites)||64 (12 sites)|
|Boulders||20 (3 sites)||19 (3 sites)||22 (4 sites)||61 (10 sites)|
|Bedrock||24 (3 sites)||41 (9 sites)||37 (6 sites)||102 (18 sites)|
|Total||66 (9 sites)||74 (16 sites)||87 (15 sites)||227 (40 sites)|
Turf constituents were identified with the help of a microscope and species abundances recorded using a semi-quantitative DAFOR scale (Dominant; Abundant; Frequent; Occasional; Rare). To test for differences between types of turfs (calcareous versus non-calcareous), substrata (cobbles versus boulders versus bedrock) and shore levels (low-shore versus mid-shore), PERMANOVA analyses were run on species richness (as presence/absence data) and species relative abundance data with the software PRIMER (Anderson et al. 2008). PERMANOVA combines the best of traditional test-statistics (ANOVA designs) and flexible multivariate nonparametric methods, and can thus be based on symmetric dissimilarity or distance measures (or their ranks) providing probability values (P; significant if <0.05; not significant if ≥0.05) using appropriate permutation methods. The greater the number of possible permutations, the stronger the result of the tests. The island where samples were collected was set as a random factor, as there was no hypothesis regarding differences between islands. Furthermore, SIMPER analysis on relative abundance data was used to identify the species responsible for the differences found between both types of turf.
The turf samples contained 139 species of algae from 24 orders; the Ceramiales contained 60 species, the Gigartinales 11 species, and the Corallinales 9 species. These three orders are all in the red algae (Rhodophyta). Other orders present had fewer species.
PERMANOVA tests on species composition and relative abundance upheld the basic separation into calcareous and non-calcareous turfs (Table 2).
|Source||df||P Spp. composition data/PA data||Permutations|
|Island × Substratum||4||0.001/0.001a||998|
|Island × Shore level||2||0.114/0.069||999|
|Substratum × Shore level||2||0.846/0.625||997|
|Island × Substratum × Shore level||4||0.01/0.001a||999|
|Island × Substratum||4||0.001/0.001a||998|
|Island × Shore level||2||0.006/0.037a||998|
|Substratum × Shore level||2||0.724/0.821||998|
|Island × Substratum × Shore level||4||0.001/0.001a||999|
When analysing data separately for each turf type there were no significant differences in turfs associated with substratum or shore level (Table 2).
Dissimilarity between calcareous and non-calcareous turfs is greater when comparing these using the relative abundance of its constituents (87.62) rather than using species richness (78.32). Differences between the two types of turf are mainly due to the co-dominant, erect calcareous species within one type of turf and Gelidium (dominant) and Ceramium spp. within the other (Table 3).
|Other spp.(see below)||<0.25||R|
|Other spp. (see below)||<0.25||R|
The present study validates the empirical classification of two types of turf, calcareous, and non-calcareous, based on the presence of species of Corallina, Jania and Haliptilon that occur in such abundance that they are visually recognizable (cf.Neto & Tittley 1995). Although differences between the two types of turf are mainly due to the dominance of calcareous species within calcareous turfs, Corallina elongata can also be an important constituent of non-calcareous turfs; likewise, Laurencia spp. are a noticeable component of both communities. The few other major constituents of these two types of turf differ slightly, but there is a long list of minor constituents that are common to both (Table 3) and these are mainly filamentous red algae. The definition of both turfs in the present study is in accordance with the provisional biotope definition study of Tittley & Neto (2000). However, regarding non-calcareous turf in the present study we add Gelidium microdon to the species list defined as ‘soft algal turf’ by Tittley & Neto (2000). This is the main structuring species in our non-calcareous turf samples, which is certainly due to the fact that it occurs mainly in the mid-to-low eulittoral, which coincides with the distribution reported for the association of Gelidium microdon and Fucus spiralis by Tittley & Neto (2000). Approximately 30% of the total flora of the Azores was identified within the turfs sampled for the present study.
Highly mobile substrata tend to inhibit the attachment and growth of macroalgae and favour thin, turf-like growths that are resistant to abrasion, namely fast-growing, opportunistic algae (mainly green algae and filamentous red and brown algae) that comprise non-calcareous turfs. Our finding of the absence of substratum specificities in non-calcareous turfs with increasing substratum stability (cobbles to boulders to bedrock) was unexpected (Table 2). Increased stability was expected to allow the development of more mature communities, namely turfs with a greater number of species. However, unusual stability conditions in cobble beaches as a result of reduced wave action in the summer might have allowed non-calcareous turf communities on less stable substrata to develop towards those common on more stable substrata. Accordingly, sampling at other times of year might have detected changes in communities on different types of substrata.
Species composition of both types of turf does not vary significantly in the narrow mid- to low-shore range, probably because of the limited shore extension in the Azores. Steep shores and small tidal ranges provide very little space for macroalgae to attach. A turf-like life form may present an advantage in the competition for space and help resist the strong wave action prevalent on most shores of the Azores. Other advantages of the turf life form are the retention of water, the increased surface areas for attachment of admixed algae, increased resistance to herbivory, and increased ability in vegetative propagation (Price & Scott 1992).
No hypothesis was set regarding differences in turfs sampled on different islands. Sampling was done in different years on each island and differences in species composition might reflect variations in population dynamics of the turf constituents.
The turf life form may be an ecological response to severe environmental conditions, notably wave action. Although this life form is resistant to the prevailing harsh conditions, more delicate/fragile algae, such as the filamentous species of Callithamnion and Dasya, are able to survive as minor constituents within the turf community. Turfs are an important feature of the warm temperate shore communities that dominate intertidal communities in the Azores. They thus deserve special attention, not as major features of an ecosystem, but as a local ecosystem in their own right.
The authors would like to thank Ian Tittley and the referees for editing and comments, and all members of the Phycology Group of the Marine Biology Section of the University of the Azores and students that took part in the field surveys of Santa Maria, São Miguel and Graciosa Islands. This work was partially supported by CIRN (Centro de Investigação de Recursos Naturais; University of the Azores) and Governo Regional dos Açores/Secretaria Regional do Ambiente e do Mar. Francisco Wallenstein was supported by a PhD grant from Fundação para a Ciência e Tecnologia (SFRH/BD/27466/2006). The work carried out in the present study complies with the current laws of Portugal.
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